Black Toes

Runners may enjoy many physical benefits from their exercise, such as a trim physique or great endurance. But pretty feet are not always part of the bargain.

"Runners tend to get black toe nails," said Dr. Lewis Maharam, medical director for the ING New York City Marathon and a columnist at runnersworld.com. "They can hurt and it's also embarrassing."

Black toes, known as subungual hematomas, occur when capillaries break and blood pools under the skin's surface. This often occurs in the toes because of the force of running or walking long distances. The problem is compounded if the runner is wearing shoes that are not big enough, causing the toes to constantly bang against the inside front of the shoe.

Though black toenails are unattractive and sometimes painful, they are not dangerous and will go away as the nail grows, though that can take as long as a year.

Incontinence

Incontinence can be an embarrassing but common problem among long distance runners.

Often called runner's trots or runner's runs, the problem is essentially "increased diarrhea as you are running," Maharam said.

There are two reasons runners can experience diarrhea during a long race. First, the pounding, up-and-down movement of the body moves wastes faster in the gut. Second, at a certain exertion point, the body redistributes blood flow to better support the brain, heart and leg muscles, leaving the stomach, kidneys and other organs without as much support.

Reduced blood flow to non-vital organs also explains why people often can't stomach food following an intense workout and will throw up if they try to eat.

"Always stand to the side of a runner, never to the front," Maharam said.

There are ways to minimize the problem.

"It's as simple as what goes in goes out," Maharam said, and advised not to eat fatty foods, avoid fiber the morning of a race, and forget about carbohydrate loading the night before, unless that is part of a normal routine.

"Or else you are carb unloading at mile six," Maharam said.

No Period

"Women can exercise as much as they want, as long as they fuel their body appropriately," Hoch said, and that means plenty of calories.

It sounds like the ideal advice: eat, workout and be merry.

But not fueling enough can have serious consequences. And exercising too long and too hard without replenishing lost calories can keep many women from having a normal menstrual cycle.

In fact, without proper nutrition, the luteinizing hormone pulse responsible for kicking off ovulation -- the beginning of the menstrual cycle -- can be decreased. This results in missed periods and a body clock that is thrown off.

"You need that pulse in order to ovulate," Hoch said. "If you don't ovulate, you don't have a menstrual period."